1. Field of the Invention
The present invention relates generally to a heating system. More particularly the present invention relates to a hydronic heating system using a direct-fired steam generator, two-layer packed column, secondary heat exchanger, a real-time efficiency calculation, and automatic PH control.
2. Background Art
Hydronic heating systems are commonplace in residential, commercial, and industrial buildings. Heat from the combustion of a fossil fuel is commonly transferred to the water in the hydronic heating system via conduction through fins and pipe walls, the exhaust from combustion does not come into direct contact with the heating water and is eventually vented to the atmosphere.
Another method of heating the water used in hydronic heating systems is to produce steam in a steam generator. The steam is then passed directly into the heating water which, in turn, is circulated to heat the space intended. An advantage of this latter approach is that heat can be transferred through a lesser temperature difference than the former approach. As is well known, entropy is produced by heat transfer through a finite temperature difference. Less entropy is generated when the temperature difference is reduced, and this translates into a more efficient process. However, the exhaust gases are still vented to the atmosphere, after dropping to (at best) the temperature of the return water, which is, in general, warmer than the ambient air.
When heating the water by passing steam through it, a packed column is utilized to increase the mixing of the two streams (liquid water and steam). Due to the quantity of packing material, this makes for a rather heavy boiler.
A readout, displaying efficiency or a value related to efficiency, for visual feedback, indicating a need to service a hydronic heating system would enhance the product. Unfortunately, present-day hydronic heating systems do not have such a readout.
There is, therefore, a need for a high-efficiency hydronic heating system utilizing a direct-fired steam generator for greater efficiency and with an efficiency readout. An additional need is for a packed column that is lighter than generally available, presently.
A purpose of this invention is to provide a method and apparatus for a high-efficiency hydronic heating system. To this end, a direct-fired steam generator is utilized wherein the resulting steam and the combustion products from the steam generation are all used in direct contact with the heating water. A secondary heat exchanger is used to warm incoming air used for combustion in the steam generator.
An additional purpose is for a hydronic heating system as briefly described in the preceding paragraph to have a method of eliminating excess heating water. Because the combustion products are used in direct contact with the heating water, and because water is one of the products of combustion, there will be a continuous need to remove heating water from the system. There is a need to measure this heating water removed.
Another purpose is for a visual reading of an efficiency measure for a hydronic heating system.
Still another purpose is for PH control for the water in conjunction with the direct fired steam generator method of heating the heating water in the high-efficiency hydronic heating system. Because of the presence of products of combustion in the heating water, there will be a continuous drop in the PH. This needs to be offset by the addition of a basic substance.
A final purpose is for a packed column with a reduced weight.
To improve the efficiency of a hydronic heating system, a maximum amount of heat must be removed from the combustion products. This requires that, not only should the combustion be complete, but that the products of combustion are cooled to the lowest temperature in the system. This lowest temperature is represented by the combustion air, removed from the surroundings.
To effect this heat transfer, the present invention utilizes a direct-fired steam generator. The resulting steam and the combustion products are piped into a tank containing the heating water. The steam and combustion product mixture rises through the heating water, heating the cooler return (incoming) water. The gaseous and vaporous products then continue up past a secondary heat exchanger where heat is transferred from these still-warm gaseous and vaporous products to the combustion air entering the steam generator. Thus, the products of combustion are cooled to nearly the ambient air temperature before being exhausted to the atmosphere. By returning the products of combustion to the ambient temperature within the hydronic heating system, maximum efficiency is obtained.
Because the majority of the water produced during combustion is condensed out of the combustion products, there is a continuous addition of water to the heating water supply. For this reason, water must be removed, either continuously or periodically, during operation. A water dump, for this purpose, not only eliminates the proper amount of water, it measures the quantity of water dumped. The measurement is used for calculating an efficiency of the heating system.
For visual feedback of the heating system, an efficiency is calculated. A measure of efficiency for a heating system that uses combustion for the heat required is:   η  =            Q      extr              Q      avail      
where Qextr is the heat (per unit mass of fuel) actually extracted from the fuel, while Qavail is the higher heating value of the fuel. The amount of water condensed from the exhaust is an indirect measure of the heat extracted, Qextr, from the fuel. The amount of water condensed is measured by the water dump system. Additionally, the higher heating value of a fuel is a constant for that fuel mixture. An effective measure of the efficiency of the present hydronic heating system, then, is:                               η          e                =                  k          ⁢                                    w              ext                                      f              burned                                                          (        1        )            
where wext is the mass (or weight) of the water dumped, and fburned is the mass (or weight) of the fuel burned. A constant, k, may be used to scale the result to a desired range. An aspect of the present invention is a calculation of Eq. 1 in a programmable controller or similar calculation module, with a readout (digital or otherwise) for visual feedback of the heating system""s efficiency.
Along with water, a small amount of acid is produced by the combustion process. Because of the corrosive nature of water with a low PH in a heating system, a basic substance, such as soda ash or sodium hydroxide is added to raise the PH back to an acceptable level. The amount of basic substance required is directly related to the mass of fuel burned. For the present invention, a predetermined amount of basic substance is added after a known mass of fuel has been burned.
In order to improve mixing of flows from multiple streams, such as the cooler return water and the steam with combustion products, a packed column is used. The packing causes shearing in the flows, which results in turbulent flow. Turbulent flows cause substantially greater mixing than laminar flows. The packing, however, produces a heavy column. To reduce the weight of the column while maintaining complete mixing, two layers of packing are provided: an upper layer and a lower layer.
The novel features which are believed to be characteristic of this invention, both as to its organization and method of operation together with further objectives and advantages thereto, will be better understood from the following description considered in connection with the accompanying drawings in which a presently preferred embodiment of the invention is illustrated by way of example. It is to be expressly understood however, that the drawings are for the purpose of illustration and description only and not intended as a definition of the limits of the invention.